This invention relates to angioplasty and, more particularly, this invention relates to the control of the pressure in an angioplasty system.
Angioplasty is a procedure which is commonly used for dilating arteries which are occluded or blocked. Typically, a catheter is used which contains a balloon at the end which is inserted into the artery. The balloon is inflated by being filled and pressurized with a fluid from a standard syringe. The present invention is particularly concerned with a device for exerting and maintaining pressure on the syringe used to inflate the balloon catheter used in coronery angioplasty (dilatation) or peripheral angioplasty. In addition, the device is so designed to provide a vacuum resulting in the collapse of the balloon. Standard syringes of 5 cc and 10 cc volume are most commonly used to inflate the balloon catheter.
Typically, the force used to expand the balloon is exerted by hand, that is, by manually pushing the plunger of the syringe. While this force is being exerted, it is difficult to maintain constant pressure by hand. Hence, there has been a need for an apparatus to exert the force and maintain a constant pressure.
An extremely complex apparatus is disclosed in U.S. Pat. No. 4,202,346 in the name of Granier. This prior art apparatus is designed to selectively fill the catheter with different fluids for different purposes. The fluids are supplied by separate syringes and supply of the fluids from these syringes is governed by turning a micrometer screw connected to each syringe.
U.S. Pat. No. 4,370,982 issued to Riley discloses a device for controlling the pressure of fluid injected into an angioplasty catheter. This device has an outer cylindrical housing and an inner cylinder arranged in the housing to slide axially. An annular chamber is formed between the inner cylinder and the inner wall of the outer housing. A syringe is fixed to the inner cylinder. A pressure gauge communicates with the annular chamber. Thus, when pressure is applied to the plunger of the syringe to force fluid from the syringe into the catheter, the sliding inner cylinder is also caused to move axially, thereby secondarily, applying pressure to fluid in the annular chamber, this pressure being measured by the pressure gauge. Thus, the pressure shown on the gauge is, indirectly, a measure of the pressure applied to the syringe. In an alternate embodiment, a drive bolt engages a threaded bore which is to one side of, and parallel to, the syringe. A connecting lever connects the drive bolt with the plunger of the syringe.
The Riley device has a number of disadvantages, not the least of which is its complexity. The pressure is applied directly to the syringe which is fixed to the cylinder. Pressure is secondarily, therefore, applied to fluid in the annular chamber by causing the cylinder to slide within the housing. The drive bolt is connected by means of a linkage directly to the plunger of the syringe and this, also, does not provide the necessary positive pressure adjustment.